The characteristics of radiation-induced mutagenesis and carcinogenesis will be investigated in the mouse embryo cell line, C3H 10T/1/2 as well as in the diploid BHK hamster cell line. In order to determine the role of error prone repair in mutagenesis and carcinogenesis, we hope to isolate and study repair-deficient strains of these cells. Wild-type cells will be mutagenized with ethylmethane sulfonate, and repair-deficient variants will be isolated after selection by a host-cell reactivation viral suicide technique. Repair-deficient strains will then be compared to the wild-type parental cells with regard to the frequencies of mutation and transformation induced by UV and ionizing radiation delivered under varying conditions. Specific defects in DNA repair will then be characterized in each variant strain showing an altered frequency of induced mutagenesis and/or carcinogenesis, so that the role of various repair pathways in these processes can be delineated.